Production of sodium and potassium carbonates



R` D. PIKE Filed Feb. 26, 1942 .Tm mlm mlm @Tm 4 ...m

PRODUCTION OF SODIUM AND POTASSIUM CARBONATES Feb. 29, 1944.

Patented Feb. 29, 1944 Pnontio'rloNi or.' soDrUM v PorrAssIUM cannoNA'ras Robertn Pike, Pittsburgh, Paf f Application february 2 6. 1942, Serial 170,432,374

This invention` relatesl to the production of sodium .and potassium carbonates, andthis application is a continuation-in-part of .my capending application ledApril v17, 1941, Serial No.-

Avprixnary object of the invention'isto provide a simple, inexpen s ive,' easily` operable vand efficientprocess yfor'r'iroducing commercial-,IY pure' sodium carbonate and potassium carbonate from Vnatural materialssuch as wyomingiteand trona or'kindred rocks orl minerals.

A further Fobject is to provide such Aa. process y in which use isl made of trona and potassiumsilicate base exchange minerals, particularly leucitecontaining rocks. and especially wyomingite, for producing sodium carbonate monohydrate and potassium carbonate sesquihydrate.

Still another object is to `provide a process for producing in substantially pure form the aforesaid hydrated carbonates from the system corn-u prising vthe reciprocal 4salt pairs f and water, in which chlorides may occur in rela-v tively smallamounts. Y

.In the State of W'yoming'there are extensive deposits ofl a rock called wyomingite, a typical of almost pure trona (NazCOaNaHCOLZIfKIaO) a typical analysis of which is as follows: Y

t Per cent -NanCOs v v 49.29 NaHCO3-.. Q 33.18 H2O y v Y 17.07 Water insoluble 0.30 f cl` Y v i 0.03 sm y v.."lracey 'Ihe` invention of my aforesaid copending application is in part predicated upon my discovery that wyomingite or similar roel:` may be reacted with trona or thelike to eiIect basee'xchange of the potassium oi the-wyomingite and produce potassium carbonate which'di'sso'lves, as it is formed. in the sodium carbonate liquor providedv by the trona, and further that by appropriate treatment it is possible readily torecover therefrom theV two carbonates separately and in commercially pure form. Although inthe practice of that inven tion vtrona may be'heated to decompose the sodium bicarbonate presentin the rock, and the wyoominsite then treated separately with asolution of the resultant sodium carbonate, the applica-- tion describes it as preferable to effect the decomposition in a suitable reaction vessel which is initially charged with raw trona, wyomingite and waterso that the wyomingite base exchange reac- Approximately onelhalt ot wyomngite consists o! the mineral leucite (KzOAhOaASiOz) which is the only potassium silicate mineral known that is amenable to'base exchange betweenfits potas` Vsium content and sodium ion. lfDue to this property about 8 pounds of K10 per 100 pounds of wyomingite are available for base exchange with sodium. 1

'The principal deposit of wyomingite lain-"Zirkel Mesa, near Superior, Wyoming, about 40 miles easterly from the town of Green River. -About 20 miles westerly from Green River are large beds tion then follows without interruption. For optimum efllciencyfa considerableexcess of sodium carbonate is present because this assists in recovering the maximum amount ofthe available potassium 'content or the wyomingite. s

The reactions involved are aslollows:

Trona decomposition:`

' 2Na2COLNaHCOa-*3NaaCO3H20-i-CO2 Baseexchanse: Q. f

where the term .'rNagCOz refers tothe excess of this compound which lisy used to cause the base exchange reaction to go to" conripl'etion.A

j After thebase exchange' reaction hasZ been completed the solution is separated-'from insoluble matter, such as wyomingite tails. and i's'- then subjected tol concentration `by-revaporxettion, Vpreferably lin a multiple effect evaporator. `In this y manner the solutionor mixed-carbonatos may be concentrated to a point where sodium vcarbonate monohydrate '(NanCOalHaO) will be salted out inr substantially pure form. By further concentration there is then crystallized an amount ot the lo t . tion is then returned to the last'evaporator ei- The present invention is predicated in part,

therefore upon the discovery that it is advantageous to eect certain mod iiications in and gimf pliiications of the process disclosedfin my 'said application Serial No. 388,951. It is, j predicated also in part upon treatment ci the raw potassium carbonate solution to free it irom combined chlo-` rine which enters from the trona and may, if not removed. render the products unsuitecl for some The invention will be described further withr reference to the accompanying drawing of which Fig. .l is a schematic how sheet of the cold circulating mother liquor from the K2CO3.11/2H2O crystals. This mixed liquor is then passed through a water cooled crystallizcr to crystallize out the KCl, which occurs almost completely, thus removing substantially all oi the chlorine introduced into the circuit by the trona or otherwise. The KCl is removed thereby so` completely, that none can crystallize out With the potassium carbonate sesquihydrate.

The mother liquor from the KCl crystalliza fect where a quantity of the double salt, NaBLCOa, may be salted out down to the point (isothermal invariant point) where KrCOsl/ZI-r@ comes out #with it; At, or near, this point evaporation is '"stbpped and the solution is cooled, say to about 25au C. to crystallize out the potassium carbonpreferred embodiment of this invention; and Y Figc?! a graph illustrative oi the solubilityrelationships of Vthe system. potassium carbonate,

sodium carbonate, and cutter.`

In accordance with the present invention the ravvV trona is preferably calcined, e. g., at 500 to 100G Furto convert the soduim bicarbonate to sodium carbonate. An aqueoussolution of the calcined trona is then prepared and added to a charge of wyomingite, ground to pass a 16- mesh screen, in an autoclave, the solution be ing used in an amount such as to provide a considerable excesswof sodium ions over the `arriount theoretically required by the oregcing equation. The charge is then heated in the closedv Y autoclave to effect the base exchange reaction,

as by heating it for about 3 hours vunder a steam pressure of.2 pounds.l `This producesabrine containing sodium carbonate and potassium carbonate (equivalent to about pounds of KaO per 100` pounds of wyomingite), together with small amounts oi?v chlorideand traces of sulfate. The sulfate may be removed from the brine at this point, aiterseparatlon of insoluble matter,

by treatment with a very ysmall amount or barium chloride. l f

At this stage the brine is not saturated with sodium carbonate and it has now been found to be advantageousy to enrich itin sodium carbonate, particularly up to the saturation. point of the hot brine, which' may be done by addingV up to about 9 poundsv of sodiumcarbonate as calcined trona. per pound of Kao recovered in the brine. 'I'his sodium carbonate is recovered` as the monohydrata and' as the water rof the brine must be evaporated in any event its prot ate sesquihydrate in substantially pure iorrn. Thevmother liquor is returned to the circuit via the KCl crystallizer in the manner just described. A

o The chloride content of the trono. is so low that the KCl crystallization step' described may be omitted if it is unimportant that the potas- 'siurn carbonate carries a small 'amount-of KCl,

yrioritrially less than 0.5 per cent. In 'such event the crystallization of NaKCOs will follow directly that 'of the sodium carbonate. However, the'in'clusion of the KCl removal step' is usually desirable ,toproduce KzC'Oa `of a purity acceptable for most purposes and to provide against a duction entails nosignicant added cost apart from that of calculation' of the trona.

' Preferably the evaporation is conducted iny multiple effect evsporstors so arranged that the vapor pressure will increase substantially as the solutions becomel more concentrated with KzCOa, which is of assistance in separating the two carbonates. By following this Vprocedure.

NanCOsl-LO is salted yout nrst in substantially pure form. andl evaporation is carried out almost tothe point where NaKCO: begins to crystallize. All or a part of the mother liquor may then be removed. and partly cooled by adding it to the possiblev larger'addition of NaCl to the circuit.

The invention may be described in vfurther cle- Y tail with reference to the drawing. Having referu ence" to Fig. 1, wyomingite ground to pass a 1G- mesh screen is charged from aV storage bin l into an autoclave 2. -Raw trona is calcined in a furnace 3 toconvert the NaHCO: to NarCOa, and the `product may be stored in a'bin 4 from which itis withdrawn according to need into a tank 5 clave, Vwhich may be provided interiorly with lifter venes. Under such conditions4 the base exchange reaction will usually be completed in about three hours after the charge has reached its full temperature. i Y 1 After the-completion oi the base exchange reaction steam may be bled from the autoclave to heat a further charge of Water for *tank 5, the last 2G pounds, Aor so, beingused to blow. down the contents of the autoclaveto a iilter 6,' suitably of the sand type in which the solids forni their ovm lter medium. Ihe cake of insoluble residue, largely sodium leucite with other inert, insoluble material, is discarded as tailings. The clear hot brine, containing sodium and potassium carbonatos, togetherv with the wash water is then passed to a tank 1 Where additional calcined trona may be added to form the l carbonate for al particular use may vbe -so great that it need not be recycled asdescribed but may be removed with the sodium carbonate. vAlthough the NaKCOa is shown as being dissolved in the original evaporator feed, it may be introduced into the evaporator circuit at some other convenient point.

l2843,031 d quadruple eiect evaporatoris preferably.

used, with the ilrst eiiect split, giving ilveeiects in all. In Fig. l thev split effect is indicated at E-l, E-la, and theotherthree eiecis at E2,

E-t, and E-d, feed from tank t enters E-t and Y passes to lll-ll, or vice versa. It passes from there successively to lll-Zand .El-wirr.. Ifsulcient calcined trona has been added in" tank. l,

sodium carbonate will crystallize out in all four.

edects, E--ll, itl- 3, E-2 and E-la, lout as illusthe line GH. KCl would come out kalong this line if it had not been removed at F'. I

In the production ci, one ton of KzO in the Vform of, potassium carbonate sesquicarbonate trated only E-ld isy equipped to handle a con sidera-ble amount of i, crystallization.l This is done by circulating the liquor from E-iathrough a settler 9 from which the uncierllow`AA goes to a feed tank lll for the sodium carbonate The major partnof the overoW-froxn- K filter il. settler e is returned to E-la vthrougl'x a feed xiti.

from the wyomingite and trona of the foregoing vanalyses there would be charged into the auton :clave 4.15 tons ci sodium kcarbonate or its equivaient incalcined tronc., 13.9 tons of wyomingite, and 29.8 tons of hot water. Ii no calcined trona is added to the evaporator feed therewill be produced about 3.03 tons of sodium carbonate v.inonehydrate, equivalent to 2.6 tons ol? soda ash. Up to 'an `additional e tons o soda ash may loe `produced by addingtrona to the evaporator feed.l In Emia, E2, E-- and E--d the total evaporation. is 27.5 tons of water and in E--l about 2.5 tons. The amount ci double saltcircuinea is normally about 0.85 am, but may ce less.

receives also the nitrate, or mother` liquor from l .iilter li. In this way crystals of NazCOaHnQ yare prevented from accumulating in this effect.

Of course, ii there is a..heavy deposition oi crystals oi sodium carbonate monohydrate in heavy addition of trona in ytanlr l, they should 'be equipped with a similar circulatory lter system. I 1- i The balance of the overflow from settler d, or

the netfiiow, goes in part .to acrystallizer it f which also receives through a feed tank ifi the cold mother liquor from the crystals of With the potassiumcarbonate sesquilnfdrate mother liquor there iscirculateci 2.45 'tons ci water with 2.67 tons ofKaCOa in solution. in

the operation described, the amount oiV KCl crystallized .varies from about 8 pounds when no calcined trona is yadded to the feed to a maxi mum ot about 25 pounds per ton oi'KzO when Y, 'the feed is saturated with trono..

The use of Wyoming trona is desirable because A of the fact that it contains only a trace of sul fateg'ancl also this is` preferably removed because any accumulation oil--NazSOr` in the cycle will j tend to add-it toboth the potassium and the sodium carbonatos. Y

According tothe provisions oi the patent statutes, I have explained the principle and method of practicing my invention and have ldescribed what I now consider to represent its best embodiment. However. I desire to have it under stood that, within the scope of the appended Eiiluent from E-l passes to a settler 2t. The Y.

underflow, containing crystals of NaKCOs, goes to filter I9 from which the crystals are returned to feed tank il. The overilow from settler goes in part to a crystallizer 22 where' K2CO3.1 MaI-1z0 is crystallized for recovery on a filter 23. The major part of overflow from 2li is passed to feed tank l 8 for return to E-I.

E-l and E-la are supplied with steam at about pounds gauge pressure, although the steam may be supplied at higher or lower pressures. The vapors from E-l and E-la are'fed to E--2.

The progress of the individual stages of the concentration process involved may be described most simply with reference to Fig. 2i.. The composition of the raw brine from lter t is repre sented by the point m, and calcined trona is dissolved in it along mn. Evaporation begins at n and proceeds nearly to F in E--la, E2, E-3 and E-4, with deposition of sodium carbonate monohydrate. At this point the cycling mother liquor from the potassium carbonate sesquihydrate is added, bringing the liquor to F', when the liquor is treated to crystallize out the KCl. Evaporation is then resumed in E-l along the line 'F'F". The double salt is crystallized out in E-I along line FG. Evaporation is stopped at or near G, which is known as an isothermal invariant point, and after separation from the v NaKCO; the solution is cooled to 25 C., producing potassium carbonate sesquihydrate along claims, the invention may be practiced otherwise than as specilcally described.

I claim:

1.111 a method of producing potassium caru bonate from wyomingite and crude sodium carborlate` whichcomprises heating iin a 'closed chamber wyomingite, water and said crude carbonate in anamount to supply sodium carbonate in substantial excess of that stoichio metrically needed for base exchange with the available potassium of the Wyomingite and thereby producing potassium carbonate, sepa-'- rating the resulting raw brine from solids, dissolving a further amount of sodium carbonate vin the raw brine to form an evaporator feed,

clarifying said brine, then evaporating said brine to crystallize sodium carlaonate until the brine approaches saturation with respect to so dium potassium carbonate, removing and recov-n ering the crystallized sodium carbonate, evaporating the resulting mother liquor further and crystallizing out said sodium potassium car-s bonate to the point where it and potassium car bonate containing a minor amount of common salt which comprises heating in a closed chamber wyomingite, water and said crude carbonate in an amount to supply sodium carbonate in substantial excess of that needed stoichiometrically for base exchange with the available potassium of the wyomingite and thereby producing potassium carbonate, separating the resulting brine from solids, dissolving in said brine a further amount of sodium carbonate and then evaporating to crystallize sodium carbonate until the brine approaches saturation with respect to sodium potassium carbonate, removing and recovering the crystallized sodium car-V bonate, mixing the sodium carbonate mother liquor with sool mother liquor recovered after crystallization of potassium carbonate sesquihydrate, then crystallizing potassium chloride from the resultant mixture, separating and recovering the crystallized potassium chloride, returning the mother liquor from the potassium chloride crystallization to the evaporator and evaporating to crystallize sodium potassium carbonate to the point where it and potassium carbonate sesquihydrate crystallize together, returning the crystallized sodium potassium carbonate to the evaporator, cooling the mother liquor from the sodium potassium carbonate crytallization to crystallize out potassium carbonate sesquihydrate, and removing and recovering said sesquihydrate.

3. The method oi producing potassium carbonate from wyomingite and crude sodium carbonate containing a minor amount of common auaoai salt which comprises `heating in a closed container ground wyomingite, water and said crude carbonate in an amount to supply sodium carbonate in substantial excess of that needed stoichiometrically for base exchange with the available potassium' of said wyomingite and thereby producing potassium carbonate, separating the resulting brine from solids, then evaporating said brine to crystallize sodium carbonate until the brine approaches saturation with respect to sodium potassium carbonate, removing and recovering the crystallized sodium carbonate. mixing the mother liquor from the sodium'carbonate crystallization with cool mother liquor recovered from potassium carbonate sesquihydrate crystallization, then crystallizing potassium chloride from the resultant mixture, removing and recovering crystallized potassium v chloride, returning the mother liquor from said potassium chloride crystallization to the evaporator and evaporating to crystallize sodium potassium carbonate to the point where it and potassium carbonate sesquihydrate crystallize together, returning the crystallized sodium potassium carbonate to the evaporator,

cooling the mother liquor from the sodium po-l ROBERT D. PIKE. 

